Cast or molded concrete pipe is used conventionally for drainage purposes in connection with sewage and leaching fields in particular. This type of pipe which ranges in size from small diameters to quite large diameters has been formed conventionally by casting or molding a solid or unperforated concrete pipe, a normal type of fluid conduit, and then perforating the pipe in a convenient manner.
One way in which the perforations have been formed is to extend large cores diametrically across the molds when the pipe is formed so as to produce apertures in opposite sides of the pipe after the concrete sets in the molds and around the cores. Naturally, thereafter, it is necessary to remove the cores before the pipe can be removed from the mold. Removal frequently causes damage to the pipes resulting in an inferior product. Also, the cores can interfere with the reinforcing rods in the pipes.
A second method of forming perforations in use today is to punch or cut holes in the formed pipe. This is done indiscriminately in the field in many cases and causes damage to the reinforcing rods because as the perforations are formed the rods are often broken or cut. This provides for a weakened and damaged concrete pipe. Also, the concrete will often deteriorate around the cut or punched holes and affect the longevity and efficiency of the pipe in use. Damage to the reinforcing bars during formation of the perforations can be caused by negligence, lack of knowledge on the part of the persons forming the perforations or because the location of the intersecting bars is not known when the choice of location of the perforations is made. In the latter case, it is a matter of luck whether the perforation is made between bars or at a location of a bar necessitating the cutting or damaging of the bar or bars contacted.
In any event, formation of perforated or slotted pipe for drainage or leaching field systems by the methods known today clearly results in an inferior and undesirable product. There is clearly a need for an improved slotted concrete pipe of high quality and undamaged integrity and one which can be quickly and efficiently formed by existing pipe forming methods without materially adding to the cost of the forming process.